The mineral natural resources such as oil or gas that are used for synthesizing numerous synthetic polymers such as polyolefins are becoming ever rarer.
It is crucial to limit the use of these natural resources so as to preserve their existence and also to counter excessive price rises.
In general, power and/or telecommunications cables include coverings or insulating sheaths made of synthetic polymers such as polyethylene, polyvinyl acetate, or polyvinyl chloride.
Document JP 2004-311063 describes a power cable having an extruded layer of a biodegradable polymer, and in particular of a polylactic acid.
Nevertheless, it is important to be able to diversify the number of extrudable polymer compositions that make limited use of synthetic polymer, or that do not include any synthetic polymer at all, and that present thermomechanical characteristics that are at least similar to those of compositions that already exist on the market for cable applications.
Thus, the technical problem to be solved by the subject matter of the present invention is to propose a power and/or telecommunications cable that includes at least one component element made of a material extruded from an extrudable composition that makes it possible to avoid the problems of the prior art, in particular by offering compositions constituting alternatives to compositions of the prior art.
Thus, the Applicant has carried out intensive testing to discover compositions that enable a significant limitation to be achieved in the use of synthetic polymers, while maintaining mechanical, insulating, and fire-retardant properties that are identical to, or even better than, the properties of prior art cable sheaths.
According to the present invention, the solution to the technical problem posed lies in that said extrudable composition comprises a biopolymer selected from polymers of cellulose ester, polymers of starch complexed with a biodegradable polyester, polymers of polyhydroxyalkanoate, and/or polymers of polylactic acid comprising a mixture of polylactic and of polyester.
The term “biopolymer” means that the carbons of said polymer come from renewable biological sources.
As examples, the biopolymer may be extracted directly from biomass, it may be regenerated from biomass by fermentation or by hydrolysis, or it may be obtained by microbial transformation of biomonomers.
Most biopolymers are biodegradable, in other words, under the action of enzymes from microorganisms, they decompose into carbon dioxide, methane, water, and inorganic compounds.
Cellulose or cellulose-based polymers are generally produced by chemical modification of natural cellulose.
Cotton and wood are materials from which cellulose is produced industrially.
Starch or starch-based polymers are thermoplastic polymers coming from chemical, heat, and/or mechanical treatment of starch.
Starch is to be found in numerous plants such as maize (corn), wheat, legumes, roots, tubers, and rhizomes such as potatoes and cassava.
Polyhydroxyalkanoate or polyhydroxyalkanoate-based polymers are produced naturally by bacterial fermentation of sugars or lipids and they can have thermoplastic or elastomeric properties.
The general formula I for polyhydroxyalkanoates is as follows:
in which:                R may be a hydrogen atom or a C1-C16 hydrocarbon chain; and        x is an integer greater than or equal to 1.        
Polylactic acid or polylactic acid-based polymers are aliphatic polyesters produced from maize starch.
In a particular embodiment, said extrudable composition also includes a synthetic polymer, preferably selected from polyethylene, polypropylene, ethyl vinyl acetate copolymer, polyvinyl chloride, and polyester, and mixtures thereof.
According to a characteristic of the present invention, each component element of said cable is selected from an insulating covering, a protective sheath, and a cable-filler material.
Whether a cable is electrical or optical, for transporting power or for transmitting data, it is essentially made up of at least one electrical or optical conductor element extending inside at least one insulating element.
It should be observed that at least one of the insulating elements may also act as protection means and/or that the cable may also have at least one specific protection element forming a sheath, in particular for electric cables.
Furthermore, when it includes a plurality of insulating electric conductors, a cable may further include a cable-filler material that serves essentially for holding said insulated conductors in place.